The need of data transmission capacity has grown remarkably during the last years. Since most subscriber lines are twisted pair cable, originally designed for voice transmission, new techniques have been developed to increase the capacity of subscriber lines for satisfying continually growing demands. Different DSL (Digital Subscriber Line) techniques even reach transmission speeds of several Mbit/s. Especially, ADSL (Asymmetric Digital Subscriber Line) has become popular.
There are some problems in the ADSL technique. Pair lines considerably attenuate the signals on ADSL frequencies (25-1100 kHz), when the attenuation is at the strongest level at the high frequency end of the bandwidth. The attenuation also depends on the distance between an exchange and customer. In an urban area, where most customers are, the maximum capacity can be achieved (inside a distance of about 2 km from the exhange) in most cases. Customers inside the distance of about 5 km from the exhange can be reached by ADSL but not at maximum capacity.
Another problem is that a twisted pair line has to transmit both the original POTS (Plain Old Telephone System) traffic and the ADSL traffic. One solution is that the distribution network in a customer's premise is divided into two parts: the part for POTS traffic and the other part for ADSL traffic. In other words, at least one pair line is allocated to the ADSL traffic. The division of the lines is done in a distribution cabinet at the customer's premise wherein a splitter is installed. FIG. 2 shows an example of a divided distribution network. The splitter 10 is inside the cabinet 13, which also contains the distribution cabinet 1. One pair line 8 forms a distribution network for POTS signals, and the other line 9 forms a distribution network for ADSL traffic. An ADSL station 7, which uses ADSL as a transmission technique, is connected to an ADSL modem 5 (inside or outside the terminal), which in turn is connected to a telephone socket 3.
The installation of the splitter and the division of the network requires a visit from an installer, which increases the operator's costs and is annoying for the customer. At present, operators prefer self-installation solutions wherein customers can make installations themselves. FIG. 1 shows an example of a self-installation. The incoming ADSL traffic is distributed from the distribution cabinet 1 through the distribution network 2, i.e. through a normal pair line, POTS terminals 6 are connected to low-pass filters 4, which are connected to telephone sockets 3. The low-pass filters protect the POTS terminals against ADSL signals, which can be interfering, and vice versa. The ADSL station 7 is connected to the ADSL modem 5 (an external or internal element), which is connected to the telephone socket 3. Both the low-pass filters and the modem should preferably be installable without tools.
A new interesting area has recently come out. The number of customers, who have more than one computer, has become greater and greater. Often, these customers want to connect their computers, forming a home network. It is also to desired to connect the computers to the Internet. There are several techniques offering home networks, such as wireless LANs, techniques using power supply networks, and techniques using twisted pair line networks. A technique, called HomePNA (Home Phone Networking Alliance), is the technique of using POTS networks.
The Home Phone Networking Alliance aims to achieve a home network structure wherein no changes are needed in physical transmission media. HomePNA utilizes POTS lines in a customer's premise. HomePNA performs LAN (Local Area Network) through which the customer's computers can communicate with each other. The LAN also makes it possible to divide the Internet connection with devices connected to the LAN, such as computers and printers. FIG. 3 shows an example of HomePNA. A gateway 31, such as a cable modem or ADSL modem, performs a connection between the Internet and HomePNA.
Since HomePNA is a technique utilizing POTS lines, it is safe. Transmission lines are inside the customer's premise, and the only connection to the outside world is the gateway. That is not possible when using wireless or power supply transmission, since in these cases the transmission media carries traffic of several customers. It is possible to encrypt the traffic, but congestion may occur when several customers use the same transmission media. Briefly, HomePNA seems to be a good technique for forming a LAN in a customer's premise.
However, there are some difficulties in realizing a HomePNA network, particularly when a customer is an ADSL subscriber. The Home Phone Networking Alliance prefers that customers do not need to install any filters to their telephone sockets as illustrated in FIG. 3. This may work nice if a customer is a POTS subscriber (the gateway to the outside is a cable modem and the subscriber loop is a POTS line), but if the customer is an ADSL subscriber (the gateway to the outside is an ADSL modem and the subscriber loop is an ADSL line), the situation is much more complex. For example, low-pass filters should be installed at the telephone sockets as illustrated in FIG. 1.
An ADSL line is very sensitive to external loads—especially a nonlinear load is fatal. HomePNA stations look like capacitive and nonlinear loads to an ADSL line. FIG. 4 shows an example of the equivalent circuit of a HomePNA station (version 1.0/1.1) seen from an ADSL line. As can be seen, the station performs a serial LC resonator, which generates a zero impedance at the frequency range of ADSL, as shown in FIG. 5. The ADSL frequency range is from the upper end of the POTS frequency range (about 4 kHz in POTS and 100 kHz in ISDN) to about 1.1 MHz as illustrated in FIG. 6.
The aim of this invention is to eliminate the above-mentioned drawbacks and to offer an as easy as possible solution to perform a LAN inside a customer's premise utilizing POTS lines, when the customer is an ADSL (or possibly another type of xDLS) subscriber.